The present invention is directed to a system for augmenting power in gas turbines. In particular, the present invention is directed to a system for providing both power augmentation and evaporative cooling in gas turbines.
Gas powered turbines are utilized in a variety of useful applications. Gas turbines are frequently used in marine applications, power generation and chemical processing. Land-based gas turbine power generation facilities can also provide combined cycle benefits when a heat recovery unit is utilized to generate steam from the exhaust gas generated by the turbine and a steam turbine is then operated by that steam.
The term xe2x80x9cgas turbinexe2x80x9d traditionally has referred to any turbine system having a compression section, combustion section and turbine section. In recent years, the term xe2x80x9ccombustion turbinexe2x80x9d has more frequently been used to reference the technology. In this regard, the term xe2x80x9cgas turbinexe2x80x9d as used herein represents both the traditionally used term and the term xe2x80x9ccombustion turbinexe2x80x9d.
Gas turbines typically comprise a compressor section for compressing inlet air, a combustion section for combining the compressed inlet air with fuel and for oxidizing the fuel, and a turbine section where the energy from the hot gas produced by the oxidation of the fuel is converted into work or power. Typically, in operation, natural gas, kerosene or synthetic gas (such as carbon monoxide) is fed as fuel into the combustion section. The rotor, comprising a rotor shaft, attached turbine section, rotor blades and attached compressor section rotor blades, then mechanically powers the compression section or a compressor used in the chemical process or electrical generation. The exhaust gas from the turbine section can either be used to achieve thrust or serve as a source of heat or energy. In some cases, the exhaust gas is discarded.
Certain turbine sections employ the use of fluid-cooled rotor blades for either pressurized air, steam or the like, which is then passed through internal cooling cavities within the rotor blades which are used in the turbine section. This facilitates higher temperature output from the combustion section.
Moreover, gas turbine compressors must be cleaned periodically to remove the build-up of particulates on internal components. Some of this cleaning can be performed without a full shutdown of the gas turbine, and materials such as water, ground pecan hulls, or chemical cleaning mixtures can be either sprayed, blown, or otherwise input into the inlet of the gas turbine after the gas turbine has been operationally configured for such a cleaning operation. Such a chemical mixture is disclosed in U.S. Pat. No. 4,808,235 entitled xe2x80x9cCLEANING GAS TURBINE COMPRESSORSxe2x80x9d issued on Feb. 28, 1989 to Woodson, et al. Other systems for minimizing build-up of particulates on internal components of gas turbines focus on cleaning of the gas turbine inlet air as is, for instance, disclosed in U.S. Pat. No. 4,926,620 entitled xe2x80x9cCLEANING GAS TURBINE INLET AIRxe2x80x9d issued on May 22, 1990 to Donle.
Materials such as water can also be added when the gas turbine is operating under full load to augment the power output capability of the gas turbine above the output achievable with humidified air. This is referred to as xe2x80x9cwet compression.xe2x80x9d Wet compression enables power augmentation in gas turbine systems by reducing the work required for the compression of the inlet air. This thermodynamic benefit is realized within the compressor of the gas turbine through xe2x80x9clatent heat intercoolingxe2x80x9d, i.e., where water (or some other appropriate liquid) added to the air inducted into the compressor cools that air, through evaporation, as the air with the added water is compressed. The added water effectively functions as an xe2x80x9cevaporative liquid heat sinkxe2x80x9d in this regard.
The wet compression technique thus saves an incremental amount of work, which would have otherwise been needed to compress air not containing the added water, and provides an incremental amount of energy available to either drive the load attached to the gas turbine (in the case of a single shaft machine) or to increase the compressor speed to provide more mass flow (which can have value in both single shaft and dual shaft machines).
An additional incremental contribution to power augmentation is also realized in the turbine section by a small increase in mass flow provided by the added vaporized liquid. A further incremental contribution to power augmentation also arises from an increase in air flow which has been noted to occur with a first injection per minute increment of water in a large land-based power gas turbine. This rate may vary according to engine size. It should be noted that additional fuel is required to raise the temperature of the cooled air/steam mixture discharged from the compressor to the firing temperature of the gas turbine. However, the net energy realized from the wet compression effect is greater than the energy cost of the additional fuel needed, resulting in a net addition of power to the system as a whole.
The power augmentation benefits of wet compression have been well discussed in the prior art. As noted by David G. Wilson in xe2x80x9cThe Design of High-Efficiency Turbo-machinery and Gas Turbinesxe2x80x9d (1984, Massachusetts Institute of Technology), a six stage centrifugal compressor used in a 1903 vintage turbine built by Aegidius Elling injected water between compressor stages.
Also in the 1940s, an overview of the principles of wet compression were reported by xe2x80x9cWater Spray Injection of an Axial Flow Compressorxe2x80x9d by I. T. Wetzel and B. H. Jennings (Proceedings of the Midwest Power Conference, Illinois Institute of Technology, Apr. 18-20, 1949, pages 376 to 380); which is incorporated by reference herein for purposes of describing the background of the present invention. The Wetzel and Jennings article teaches the use of xe2x80x9cwater . . . sprayed into the inlet duct just upstream from the compressor through four nozzles.xe2x80x9d No actual results using a gas turbine, however, were reported in this article.
In the development of jet aircraft, wet compression power augmentation using alcohol or water/alcohol mixtures has also been of interest as a method for thrust augmentation as noted in American Society of Mechanical Engineers article 83-GT-230 entitled xe2x80x9cGas Turbine Compressor Interstage Cooling using Methanolxe2x80x9d (ASME, New York, 1983) by J. A. C. Fortin and J. F. Bardon. The Fortin-Bardon article points to concerns with wet compression xe2x80x9c. . . that the liquid droplets not cause serious erosion of the compressor blades.xe2x80x9d
The above comment from the Fortin-Bardon article, and another comment in the Wetzel-Jennings article that xe2x80x9cthere was no evidence of blade erosion although admittedly the tests were of short durationxe2x80x9d help to highlight a major concern regarding liquid erosion caused by wet compression, which has contributed to preventing its full application (despite the technology""s very significant benefit). Indeed, there are a number of risks to a gas turbine system when wet compression power augmentation is used to improve its operational performance.
As noted, one risk is derived from blade erosive effects. Another problem, particularly in large gas turbine systems, relates to localized and non-uniform cooling problems due to the non-uniform distribution of the added water within the compressor. This can distort the physical components of the gas turbine system in such a way as to cause damage from rubbing of the rotor against the inner wall of the housing and associated seals.
A further significant problem arises from the possibility of thermal shock if: (1) the gas turbine has essentially achieved thermodynamic equilibrium under full load; and (2) the liquid addition is abruptly terminated without feed-forward compensation to the energy being added to the gas turbine. This problem is related to a potentially damaging and abrupt transient in the internal operating temperature of the turbine section if the evaporative liquid heat sink is removed in this manner.
Another problem arises from the possibility that components of the liquid addition system may break away and impact against the relatively delicate moving parts of the gas turbine system. Still another problem is created by the fact that gas turbine components will foul from impurities in the liquid added to the compression inlet air, as these impurities are deposited on the gas turbine components as a result of evaporation of the liquid in which they had been dissolved.
With particular regard to land-based gas turbine power generation facilities and chemical processing facilities, the above risk factors, the substantial investment in the gas turbines, and non-linear, inherent scale-up considerations have collectively prevented the benefits of wet compression from being realized.
U.S. Pat. No 5,867,977 assigned to the Dow Chemical Company, discloses a wet compression power augmentation apparatus and method for adding a mass flow of water particles to a gas turbine preferably by use of a spray rack group assembly having at least one spray rack water pipe and at least one spray rack water nozzle. As taught by this patent, water mass flow is added preferably in increments such that operationally-induced thermal transients within the gas turbine are sufficiently minimized to preserve the structural integrity of the gas turbine. An optical pyrometer is used to monitor the temperature profile of fluid-cooled rotor blades in the turbine section and to detect clogging of cooling pathways in those rotor blades from impurities in the liquid added through the wet compression. The patent further discloses a novel system to guard against the possibility of icing. The patent further discloses a deformation measurement device which is preferably a laser emitter and laser target measuring system mounted to the exterior of the gas turbine housing to detect deformation in the housing of the gas turbine from associated cooling effects of the wet compression technique, and periodic addition of heat and humidity, preferably steam, to the compressor inlet.
While the system disclosed in this patent purports to disclose a power augmentation system, it does not provide adequate evaporative cooling nor an even distribution of fluid flow and mass flow balance. Moreover, this patent discloses a single location where water spray is input into the gas turbine via a spray rack. The spray rack assembly is cumbersome and interferes with the proper flow of air.
It has been shown by the present applicants that by dividing the input of water or fluid at two locations upstream of the turbine, both evaporative cooling and power augmentation can be achieved, thereby yielding a greater increase in power than provided by single station systems such as disclosed in U.S. Pat. No. 5,867,997. This eliminates hot spots and vibration. This further provides better control over droplet size because the dwell time is short. The present applicants have further designed a novel ring shaped nozzle configuration, and nozzle which provides spray without obstructing or interfering with flow of air (fluid) into the system. These and other objects of the present invention will become apparent from the detailed description which follows.